In one form of corrective eye surgery known as an epikeratophakia procedure, a corneal onlay is attached to the cornea. A corneal onlay typically comprises a central optic and an annular wing, and the wing is attached to the cornea with the optic coaxial with the optical axis of the eye.
The cornea comprises five layers, including an outer layer of epithelial cells, Bowman's membrane immediately posterior of the cells and stroma immediately posterior of Bowman's membrane. In order to properly attach the corneal onlay to the cornea, it is necessary to appropriately prepare the region of the cornea to which the wing is to be attached.
One prior art technique for accomplishing this includes removing the layer of epithelial cells and then removing a wedge-shaped annulus from Bowman's membrane and the underlying stroma. An incision is then made from the posterior end of the resulting groove radially outwardly in an annular zone to define a flap. The wing is inserted beneath the flap. For example, the wedge-shaped annulus may be cut with a trephine, and the incision may be made with a knife. The corneal onlay is attached by inserting the wing beneath the corneal flap and fixing it in place.
One problem with this technique is that it is quite invasive in that an annulus of the cornea must be entirely removed and then the cornea must be cut. In addition, the fixing of the wings beneath the corneal flaps can distort the optic and provide consequent optical distortion for the patient.
A similar prior art technique employs an annular trephine cut through Bowman's membrane and some stroma followed by a radial and circumferential knife cut from the posterior end of the trephine cut to again form a corneal flap. The corneal onlay is attached by inserting the wing on the onlay beneath the corneal flap. This technique is somewhat less invasive but does not solve the optical distortion problem referred to above.